FIG. 1 is a side view of an engine compartment 8 of a typical prior-art snowmobile 10. The engine compartment 8, located in a forward end 12 of the snowmobile 10, houses a front-mounted internal combustion engine 24 mounted to a frame 16 by at least one engine mount 24a. The engine 24 includes a crankshaft 24b driven inside a crankcase 24c by a piston reciprocating in at least one cylinder 24d. Air enters the engine via an airbox assembly 90 having an inlet 92 with a replaceable filter 94 leading to an air container 96 with an outlet in fluid communication with an air intake 25 of the engine 24. The air intake 25 typically includes an intake pipe 25a connected to a downstream carburetor 27 (or an air-regulating throttle body having a butterfly valve in the case of a fuel-injected engine). The carburetor may include an intake manifold 27a for connecting to an intake guide portion 24e of the engine. A gap G is provided beside the airbox assembly 90 to enable tool access for installation and removal of the airbox. As is known in the art, after each combustion cycle, the engine 24 exhausts through an exhaust manifold 29 and a muffler 29a. An exhaust valve drive motor 29b opens and closes an exhaust valve 29c. 
FIG. 2 is an exploded perspective view of a conventional prior-art airbox assembly 90 having both a primary airbox 100 and a secondary airbox 200. The primary airbox (which hereinafter may also be referred to simply as an airbox) includes an air inlet 102 with a flanged mouth 103. The air inlet has a downwardly curving throat formed by mating upper and lower tubular shell portions 104a, 104b. An air container is formed by mating upper and lower box-like shell portions 106a, 106b integrally formed with the tubular shell portions 104a, 104b, all of which come together to form the primary airbox 100. The primary airbox 100 further includes an air outlet 108 having a pair of outlet ports (one for each cylinder) which are connected to carburetors or throttle bodies via respective flexible tubular connections 110.
As shown in FIG. 2, the primary airbox 100 is connected to the secondary airbox 200 for receiving air from the secondary airbox which, in turn, draws air from atmosphere. The secondary airbox includes first and second side-mating shell portions 202, 204 which come together to define an enclosure or air container. The second side-mating shell portion 204 includes an inlet 206 for drawing ambient air into the secondary airbox. A replaceable filter 208 (for obstructing particulate matter from entering and clogging up the airbox) spans across the inlet 206. The inlet 206 is in fluid communication with an admission tube 210 having an oblong mouth. Sound-insulating foam 212 is installed with the admission tube 210 to minimize engine noise. As shown in FIG. 2, the second side-mating shell portion 204 includes a circular outlet 214 which is in fluid communication with the inlet 102 of the primary airbox 100. The outlet 214 of the secondary airbox and the inlet 102 of the primary airbox connect via a conically-shaped guide discharge port 220 and a foam gasket 230. The guide discharge port facilitates alignment of the outlet 214 and inlet 102 while the foam gasket provides an airtight connection between the outlet 214 and the inlet 102.
For the purposes of this specification, the term “primary airbox” refers to the downstream airbox while “secondary airbox” refers to the upstream airbox. The terms “primary” and “secondary” are thus used arbitrarily. In other words, the primary airbox could equivalently be defined as the upstream airbox whereas the secondary airbox could be defined as the downstream airbox.
FIG. 3 is a side view showing the position of the (primary) airbox 100 relative to a fuel tank 70 when both components are affixed to a prior-art snowmobile. In this configuration, the inlet 102 is oriented substantially transversely to the longitudinal axis (“travel direction”) of the vehicle whereas an outlet 108 of the airbox defines an outflow axis 109 which is generally orthogonal to an inflow axis of the inlet 102 and generally parallel to the travel direction of the vehicle. In order to provide sufficient clearance for tools to access the airbox (for installation and removal), the airbox in the prior art is mounted with a gap G between the airbox and the front of the fuel tank 70. In prior-art designs, this was seen as necessary because the engine and carburetor (or throttle body) are fixed and it was believed that the only way to remove the airbox from the carburetor (or throttle body) was to provide a gap G in order to longitudinally displace the airbox to disengage the tubular connection and the hose clamp from the carburetor (or throttle body).
As a result of this conventional design, the fuel tank was thus mounted further rearward to accommodate the needed gap G, causing an undesirable decentralization of mass. The fuel tank when full of fuel, as is understood by those of ordinary skill in the art, represents a very substantial mass which thus has a significant impact on the vehicle's dynamics. Particularly for snowmobiles, it is important to locate mass near the front drive axle or drive pulley. Therefore, the gap G between the airbox and the fuel tank results in suboptimal mass centralization and hence suboptimal vehicle dynamics.
Therefore, it would be highly desirable to provide an improved airbox that would overcome at least one of the deficiencies of the prior art as described above.